This invention relates to derivatives of the heterocyclic system known as benzo[ij]quinolizine. A further aspect of the invention relates to the use of the compounds as antimicrobial agents. Pharmaceutical compositions containing the compounds are also included within the scope of the invention.
1. Description of the Prior Art
The compound 6,7-dihydro-1-oxo-1H,5H-benzo[ij]-quinolizine-2-carboxylic acid and various derivatives thereof, including ester and salt derivatives, are disclosed in U.S. Patent Application Ser. No. 303,254 filed Nov. 2, 1972, as having antimicrobial activity. That disclosure includes other compounds having similar activity in which the benzo ring portion of the molecule is substituted by a variety of substituents in the 8, 9 and 10 positions, and the alicyclic ring is substituted by methyl, ethyl, or trifluoromethyl groups. These compounds do not contain any functional substituents on the alicyclic ring.
2. Description of the Invention
This invention relates to certain 6,7-dihydro-7-hydroxy-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxylic acids and ester and salt derivatives thereof. These compounds having utility as antimicrobial agents. The structure and numbering system of the heterocyclic system of these compounds are ##STR1##
Compounds of the invention are defined by the formula ##STR2## wherein R.sup.1 is hydrogen, methyl, or ethyl; R.sup.2 is methyl, ethyl, methoxy, halogen, hydroxy, nitro, amino, acetamido or formamido; n is zero, one or two, and when n is 2, R.sup.2 may be methylenedioxy ##STR3## bonded to adjacent carbon atoms; and when R.sup.2 is ethyl, methoxy, nitro, amino, acetamido or formamido, and n is 2, each R.sup.2 must be different; and lower alkyl esters and pharmaceutically acceptable salt derivatives of said acids.
The terms "lower alkyl", "alkyl" or the abbreviation "alk" as used herein refers to straight and branched-chain alkyl groups having 1 to 4 carbon atoms.
It is well known in the art that pharmaceutically acceptable salts such as alkali metal, alkaline earth, aluminum, iron, and other metal and amine salts can be readily formed from biologically active acids. These salts are essentially equivalent to the acids with respect to biological activity, and in some respects may even offer advantages over the acids in absorption, formulation and the like due to their increased water solubility.
Salts of the free acid compounds of the invention are prepared by reacting the corresponding acid with a base and evaporating to dryness. Inorganic bases or organic bases such as sodium methoxide or an amine may be used. Presently preferred salts are alkali metal and alkaline earth salts.
The free acid compounds of the invention are preferred in that they exhibit the highest levels of antimicrobial activity.
The lower alkyl esters and salts of the acid compounds are useful as intermediates for the preparation of the corresponding acids, and in many cases these esters and salts are also useful as antimicrobial agents. The preferred esters are ethyl esters.
Compounds of formula 1 wherein R.sup.1 is methyl or ethyl represent a preferred subclass of antimicrobial agents. Also preferred are compounds wherein n is one and R.sup.2 is halogen, methyl, methoxy or hydroxy. When R.sup.2 is halogen, it is preferably fluorine, chlorine or bromine. Another preferred subclass of compounds is that wherein n is two and R.sup.2 is methylenedioxy or ethylenedioxy bonded to adjacent carbon atoms.
Compounds of formula 1 wherein R.sup.2 is nitro or amino are particularly useful as intermediates for the preparation of other compounds of the invention.
All compounds of formula 1 will have at least one optically active center at the 7-position. Compounds wherein R.sup.1 is methyl or ethyl have an additional optically active center. Thus, compounds of the invention may have up to four or more optical isomers. Pure optical isomers of the compounds may be synthesized, but the process is tedious and economically impractical using presently available techniques. Although it has been found that in some cases, one isomer may have more antimicrobial activity than another, sufficient activity is obtained with a compound containing a mixture of isomers so as to make isolation of the individual isomers unnecessary. Since the acid compounds of the invention have a reactive hydroxyl group in the 7-position and a reactive acid group, they have potential utility as monomers for making certain polyesters.
The antimicrobial activity of the compounds of the invention can be demonstrated by the known, standard plate dilution method for bacterial susceptibility to antibiotics. (See English Antibiot. Chemother, Vol. 1, 118, 1951.) The culture medium employed permits susceptibility testing of fastidious microorganisms toward antibiotics, sulfonamides, and other chemotherapeutic agents. Tryptone soy agar (oxoid) of the following composition is the culture medium.
______________________________________ Oxoid tryptone 15 g Oxoid soy peptone 5 g Sodium chloride 5 g Oxoid agar-agar No. 3 15 g Water 1 liter ______________________________________
Using this test, the compounds of the invention have been found to have a broad spectrum of activity against gram-positive and gram-negative microorganisms.
The compounds of the invention are active against microorganisms either in the absence or presence of ten percent horse serum.
In the test procedure the amount of a compound required to give complete, partial, or no inhibition of microbial growth on the agar plates is determined. The compound selected for evaluation is added to the agar medium to give concentrations of one, ten and one hundred milligrams per liter. A series of plates is prepared with these concentrations, and each series includes control plates containing only agar. Ten percent horse serum is added to one series of such plates. Aliquots of broth culture of each of eleven species of microorganisms are innoculated onto the plates. The plates are incubated at 37.degree. C in a ten percent carbon dioxide atmosphere for 18 to 24 hours. The microbial growth on each plate is read visually, and minimal inhibitory concentrations are recorded.
The microorganisms for this test were:
1. Stapylococcus aureus PA1 2. Bacillus subtilus PA1 3. Pseudomonas aeruginosa PA1 4. Escherichia coli PA1 5. Streptococcus sp.* PA1 6. Aspergillus niger PA1 7. Candida albicans PA1 8. Mima polymorpha PA1 9. Herellea vaginicola PA1 10. Klebsiella pneumoniae PA1 11. Streptococcus fecaelis FNT *Strains isolated from dental caries in rats or hamsters at the National Institute of Dental Health and grown in PFY or APT agar.
Some of the compounds of the invention have also shown activity toward anaerobic bacteria, e.g., Bacteroides sp. and Clostridium welchii.
It will be understood by those skilled in the art that the species used are representative indicator species, as it would be impractical to screen against all bacteria. It is well known in the art that broad spectrum activity can be predicted on the basis of activity shown against selected representative bacterial species.
The compounds of the invention are active against microorganisms in vitro or topically. In vitro activity is useful in itself since antimicrobial agents may be used as components of disinfecting solutions for disinfecting items such as medical and dental equipment. The preferred compounds of the invention are also active in vivo in animals.
Many of the compounds of the invention are active when administered orally to animals. They are excreted in the urine, and are useful in treating urinary tract bacterial infections in mammals. An advantage of the compounds is that they appear to be conjugated to a minimal degree by the mammalian organism. Because the compounds are not significantly inactivated by normal metabolic processes, higher levels of the active forms of the compounds can be maintained in the blood and urine.
The acute oral toxicity of the preferred compounds of the invention is generally moderate to low compared with the effective oral dose, and they have a fair to excellent therapeutic ratio.
Presently preferred compounds of the invention have a broad spectrum of antimicrobial activity and a good therapeutic ratio (LD.sub.50 /ED.sub.50).
These compounds are:
9-chloro-6,7-dihydro-7-hydroxy-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxyli c acid; PA0 6,7-dihydro-9-fluoro-7-hydroxy-5-methyl-1-oxo-1H,5H-benzo[ij]-quinolizine-2 -carboxylic acid; PA0 9-chloro-6,7-dihydro-7-hydroxy-5-methyl-1-oxo-1H,5H-benzo[ij]quinolizine-2- carboxylic acid; PA0 6,7-dihydro-7-hydroxy-5-methyl-1-oxo-1H,5H-benzo[ij]quinolizine-2-carboxyli c acid; PA0 6,7-dihydro-5,9-dimethyl-7-hydroxy-1-oxo-1H,5H-benzo[ij]quinolizine carboxylic acid; PA0 6,7-dihydro-9-methoxy-5-methyl-7-hydroxy-1-oxo-1H,5H-benzo[ij]quinolizine-c arboxylic acid; and PA0 6,7-dihydro-5,8-dimethyl-7-hydroxy-1-oxo-1H,5H-benzo[ij]quinolizine-2-carbo xylic acid.
The acidic compounds of the invention are ordinarily white or yellowish to brown crystalline or amorphous materials when purified. They are substantially insoluble in water, lower alcohols or hydrocarbons and are more soluble in halogenated solvents and dimethylformamide and the like. The esters are generally somewhat more soluble in organic solvents. The alkali metal salts have appreciable solubility in water and lower alcohols.
The compounds of the invention may be formulated by incorporating them into conventional pharmaceutical carrier materials, either organic or inorganic, which are suitable for oral or intraperitoneal application. For in vitro or topical use, simple aqueous solutions or suspensions are most conveniently employed. For this purpose, concentrations of the order of 100 parts per million up to about 5 parts per thousand are suitable. The formulation is used by immersing objects to be treated therein, or by local application to an infected area.
The amount of compound to be used, for example, in the treatment of a microbial urinary infection by oral administration, will be an effective amount less than a toxic amount. The amount to be administered to control an infection will depend upon the species, sex, weight and physical condition of the patient as well as other variable factors. This judgment is well within the skill of the medical practitioner. Usually the amount will be less than 100 mg/kg per dose. Conveniently this dose is administered in the form of conventional pharmaceutical preparations such as capsules, tablets, emulsions, solutions and the like. Excipients, fillers, coatings, etc. are employed with tablets or capsules, as is well known in the art.
Compounds of the invention are required to contain the functional and reactive hydroxy group in the 7-position of the heterocyclic system. These 7-hydroxy compounds must be prepared from the corresponding novel 7-oxo compounds which are prepared from known starting materials through an extended and complex synthetic sequence. Several novel types of intermediates are formed during this sequence.